The present disclosure relates to selective voltage binning (SVB) of integrated circuit (IC) chips and, more specifically, to a method for improving SVB accuracy and, thereby IC chip yield and product reliability.
Manufacturing variations may cause one or more parameters to vary between integrated circuits that are formed according to the same design. These variations can affect chip operating frequency (i.e., switching speed). For example, due to variations in the equipment, operators, position on a wafer, etc., a specific parameter may vary between chips built on the same wafer, chips built on different wafers in the same lot, and/or on chips built on different wafers in different lots. If this parameter is, for example, channel length, width, or threshold voltages, the transistors of each chip may be different such that the performance varies (e.g., faster or slower). Chips that are fabricated either at the “slow” end or the “fast” end of a process distribution (e.g., a process-temperature-variation (PVT) space) may not be desirable. For example, chips that are fabricated at the “slow” end of such a process distribution may not meet the desired performance specification (i.e., may not have a fast enough switching speed); whereas chips fabricated at the “fast” end of this process distribution may exhibit excessive power and leakage current. Thus, it is possible to run faster parts at lower voltage and slower parts at higher voltage, in order to reduce the maximum power for the distribution of parts. The division between the fast and slow portions of the distribution (i.e. the cutpoint) is generally determined during the design phase.
Selective voltage binning (SVB) is a technique that was developed in order to reduce power consumption at the “fast” end of the process distribution, while increasing operating speed at the “slow” end of the process distribution. Typically, in SVB, a full process distribution for an IC chip design at a target voltage and a target temperature for the technology at issue and with respect to a target threshold voltage (VT)-type transistor is defined prior to manufacturing (e.g., based on a best case/worst case analysis) or after manufacturing (e.g., based on actual performance measurements taken from performance monitors, such as performance screen ring oscillators (PSROs), associated with the target VT-type transistor on IC chips that are manufactured according to the IC design). It should be understood that a given IC chip design will often incorporate multiple VT-type transistors (e.g., regular threshold voltage (RVT) transistors, high threshold voltage (HVT) transistors, mezzanine threshold voltage (MVT) transistors, super-high threshold voltage (SHVT) transistors, low threshold voltage (LVT) transistors, ultra-high threshold voltage (UHVT) transistors, etc.) and the target VT-type will be one of these different VT-types (e.g., MVT). Additionally, it should be understood that the performance monitors described above can be on-chip performance monitors and/or in-Kerf performance monitors (i.e., performance monitors located in the Kerf-lines between IC chips manufactured on a semiconductor wafer).
In any case, once defined, the full process distribution is then divided into successive intervals (also referred to as process windows) and different voltage ranges are assigned to each successive interval (i.e., to each process window) such that relatively low supply voltage ranges (minimum supply voltage to maximum supply voltage) within the allowable voltage range for the technology are assigned to intervals at the “fast” end of the process distribution and relatively high voltage ranges are assigned to intervals at the “slow” end of the process distribution. Subsequently, performance measurements are taken from on-chip and/or in-Kerf performance monitors of manufactured IC chips, as discussed above and, based on these performance measurements, the IC chips are sorted into different groups (also referred to as voltage bins) that correspond to different process windows. This process of assigning the IC chips to the different groups that correspond to different process windows based on their specific performance measurements is referred to as selective voltage binning. When such IC chips are shipped for incorporation into products, the voltage ranges associated with their respective voltage bins are noted. Operation of relatively fast IC chips at lower voltage ranges minimizes worst-case power consumption and operation of relatively slow IC chips at higher voltage ranges improves their performance (e.g., increases their operating speed/reduces their delay). Recently, it has been noted that some IC chips throughout the process window distribution fail to meet the performance required for their assigned voltage bin when operated near the minimum voltage allowed for that bin.